The history of philosophy is the study of philosophical ideas and concepts through time. Issues specifically related to history of philosophy might include (but are not limited to): How can changes in philosophy be accounted for historically? What drives the development of thought in its historical context? To what degree can philosophical texts from prior historical eras be understood even today?

Western philosophy has a long history, conventionally divided into four large eras - the Ancient, Medieval, Modern, and Contemporary. The Ancient era runs through the fall of Rome and includes the Greek philosophers such as Plato and Aristotle. The Medieval period runs until roughly the late 15th century and the Renaissance. The "Modern" is a word with more varied use, which includes everything from Post-Medieval through the specific period up to the 20th century. Contemporary philosophy encompasses the philosophical developments of the 20th century up to the present day.

Western Philosophy is generally said to begin in the Greek cities of western Asia Minor (Ionia) with Thales of Miletus, who was active around 585 B.C. and left us the opaque dictum, "all is water." His most noted students were Anaximenes of Miletus ("all is air") and Anaximander (all is apeiron).

Other thinkers and schools appeared throughout Greece over the next few centuries. Among the most important were Heraclitus ("all is fire", all is chaotic and transitory), Anaxagoras (reality is so ordered that it must be in all respects governed by mind), the Pluralists and Atomists (the world is composite of innumerable interacting parts), the EleaticsParmenides and Zeno (all is One and change is impossible, as illustrated by his famous paradoxes of motion), the Sophists (became known, perhaps unjustly, for claiming that truth was no more than opinion and for teaching people to argue fallaciously to prove whatever conclusions they wished). This whole movement gradually became more concentrated in Athens, which had become the dominant city-state in Greece.

There is considerable discussion about why Athenian culture encouraged philosophy, but a popular theory[which?] says that it occurred because Athens had a direct democracy. It is known from Plato's writings that many sophists maintained schools of debate, were respected members of society, and were well paid by their students. Orators influenced Athenian history, possibly even causing its failure (See Battle of Lade). Another theory explains the birth of philosophical debate in Athens with the presence of a slave labor workforce which performed the necessary functions that would otherwise have consumed the time of the free male citizenry. Freed from working in the fields or other manual economic activities, they were able to participate in the assemblies of Athens and spend long periods in discussions on popular philosophical questions. Students of Sophists needed to acquire the skills of oration in order to influence the Athenian Assembly and thereby increase respect and wealth. In response, the subjects and methods of debate became highly developed by the Sophists.

The key figure in transforming Greek philosophy into a unified and continuous project - one still being pursued today - is Socrates, who studied under several Sophists. It is said that following a visit to the Oracle of Delphi he spent much of his life questioning anyone in Athens who would engage him, in order to disprove the oracular prophecy that there would be no man wiser than Socrates. Through these live dialogues, he examined common but critical concepts that lacked clear or concrete definitions, such as beauty and truth, and the virtues of piety, wisdom, temperance, courage, and justice. Socrates' awareness of his own ignorance allowed him to discover his errors as well as the errors of those who claimed knowledge based upon falsifiable or unclear precepts and beliefs. He wrote nothing, but inspired many disciples, including many sons of prominent Athenian citizens (including Plato), which led to his trial and execution in 399 B.C. on the charge that his philosophy and sophistry were undermining the youth, piety, and moral fiber of the city. He was offered a chance to flee from his fate but chose to remain in Athens, abide by his principles, and drink the poison hemlock.

Socrates' most important student was Plato, who founded the Academy of Athens and wrote a number of dialogues, which applied the Socratic method of inquiry to examine philosophical problems. Some central ideas of Plato's dialogues are the Theory of Forms, i.e., that the mind is imbued with an innate capacity to understand and contemplate concepts from a higher order preeminent world, concepts more real, permanent, and universal than or representative of the things of this world, which are only changing and temporal; the idea of the immortal soul being superior to the body; the idea of evil as simple ignorance of truth; that true knowledge leads to true virtue; that art is subordinate to moral purpose; and that the society of the city-state should be governed by a merit class of propertyless philosopher kings, with no permanent wives or paternity rights over their children, and be protected by an athletically gifted, honorable, duty bound military class. In the later dialogues Socrates figures less prominently, but Plato had previously woven his own thoughts into some of Socrates' words. Interestingly, in his most famous work, The Republic, Plato critiques democracy, condemns tyranny, and proposes a three tiered merit based structure of society, with workers, guardians and philosophers, in an equal relationship, where no innocents would ever be put to death again, citing the philosophers' relentless love of truth and knowledge of the forms or ideals, concern for general welfare and lack of propertied interest as causes for their being suited to govern.

Plato's most outstanding student was Aristotle, perhaps the first truly systematic philosopher. Aristotelian logic was the first type of logic to attempt to categorize every valid syllogism. A syllogism is a form of argument that is guaranteed to be accepted, because it is known (by all educated persons) to be valid. A crucial assumption in Aristotelian logic is that it has to be about real objects. Two of Aristotle's syllogisms are invalid to modern eyes. For example, "All A are B. All A are C. Therefore, some B are C." This syllogism fails if set A is empty, but there are real members of set B. In Aristotle's syllogistic logic you could say this, because his logic should only be used for things that really exist ("no empty classes")

The application of Aristotelian logic is preceded by having the student memorize a rather large set of syllogisms. The memorization proceeded from diagrams, or learning a key sentence, with the first letter of each word reminding the student of the names of the syllogisms.

Each syllogism had a name, for example: "Modus Ponens" had the form of "If A is true, then B is true. A is true, therefore B is true."

Most university students of logic memorized Aristotle's 19 syllogisms of two subjects, permitting them to validly connect a subject and object. A few logicians developed systems with three subjects, or described a way of elaborating the rules of three subjects.

The history of western medieval philosophy is generally divided into two periods, early medieval philosophy, which started with St. Augustine in the mid 4th century and lasted until the recovery in the 13th century West of a great bulk of Aristotle's works and their subsequent translation into Latin from the Arabic and Greek, and high medieval philosophy, which came about as a result of the recovery of Aristotle. This period, which lasted a mere century and a half compared to the nine centuries of the early period, came to a close around the time of William of Ockham in the middle of the 14th century. Western medieval philosophy was primarily concerned with implementing the Christian faith with philosophical reason, that is, "baptizing" reason.

Early medieval philosophy was influenced by the likes of Stoicism, neo-Platonism, but, above all, the philosophy of Plato himself. The prominent figure of this period was St. Augustine who adopted Plato's thought and Christianized it in the 4th century and whose influence dominated medieval philosophy perhaps up to end of the era but was checked with the arrival of Aristotle's texts. Augustinianism was the preferred starting point for most philosophers (including the great St. Anselm of Canterbury) up until the 13th century.

During the later years of the early medieval period and throughout the years of the high medieval period, there was a great emphasis on the nature of God and the application of Aristotle's logic and thought to every area of life. Attempts were made to reconcile these three things by means of scholasticism. One continuing interest in this time was to prove the existence of God, through logic alone, if possible. The point of this exercise was not so much to justify belief in God, since in the view of medieval Christianity this was self-evident, but to make classical philosophy, with its extra-biblical pagan origins, respectable in a Christian context.

One monumental effort to overcome mere logical argument at the beginning of the high medieval period was to follow Aristotelian demonstration by starting from effects and reasoning up to their causes. This took the form of the cosmological argument, conventionally attributed to St. Thomas Aquinas. The argument roughly is that everything that exists has a cause. But since there could not be an infinite chain of causes back into the past, there must have been an uncaused "first cause." This is God. Aquinas also adapted this argument to prove the goodness of God. Everything has some goodness, and the cause of each thing is better than the thing caused. Therefore, the first cause is the best possible thing. Similar arguments were used to prove God's power and uniqueness.

Another important argument for proof of the existence of God was the ontological argument, advanced by St. Anselm. Basically, it says that God is that than which nothing greater can be thought. There is nothing that simply exists in the mind that can be said to be greater than something that enjoys existence in reality. Hence the greatest thing that the mind can conceive of must exist in reality. Therefore, God exists. This argument has been used in different forms by philosophers from Descartes forward.

Contemporary philosophical historiography emphasizes a great "gap" between Middle Ages and Modern thought. And often this "gap" is used as a mean to characterize the meaning of the word "modern" used in "modern philosophy".

However, a historical perspective (and philosophical ones less interested into a single solid "gap") emphasizes the existence of a long period of transition between the teleologically driven centuries (running up to the 13th or 14th centuries) and the rationalists-empiricists debates.
Along with the figurative arts, music, vernacular languages and literatures, and the Christian religion, philosophy was greatly renewed in The Renaissance. The Renaissance, spread throughout Europe from Italy; in particular, from Northern Italy and especially Tuscany. This cultural movement influenced not only philosophy (inaugurating new philosophical problems) but also architecture, the visual arts, and literature. Along with the concurrent Protestant Reformation, it permitted a new era of thought, independent from the Roman Catholic Church (which had dominated European thought throughout the Middle Ages).

Most medieval philosophers were priests and monks, but both early and late Renaissance philosophers were a more heterogeneous population, including rhetors, magicians and astrologues, early empirical scientists, poets, and philologists. If there was one common theme among these Renaissance thinkers it would have to be a concern for humanity (and the humanities) and the search for human specificity. The study of humanae litterae overcame that of divinae litterae, and opened the way for modern skepticism and science.

Many philosophers from the Renaissance are today read and remembered, even though often they are not categorized into a single category. In particular, those Renaissance thinkers who were especially oriented towards empiricism and rationalism (like Galileo Galilei and Machiavelli), are often seen as early Modern philosophers. On the other hand, those heavily influenced by esoteric traditions (like Giovanni Pico della Mirandola, Marsilio Ficino and even Nicholas of Cusa and Giordano Bruno) are often seen as (very) late Medieval philosophers. Only a few Renaissance thinkers who do not clearly fall into either of these categories are usually fully recognized as Renaissance philosophers, including Montaigne, Tommaso Campanella, Telesius, Erasmus, and Sir Thomas More.

As with many periodizations, there are multiple current usages for the term "Modern Philosophy" that exist in practice. One usage is to date modern philosophy from the "Age of Reason", where systematic philosophy became common, excluding Erasmus and Machiavelli as "modern philosophers". Another is to date it, the way the entire larger modern period is dated, from the Renaissance. In some usages, "Modern Philosophy" ended in 1800, with the rise of Hegelianism and Idealism. There is also the lumpers/splitters problem, namely that some works split philosophy into more periods than others: one author might feel a strong need to differentiate between "The Age of Reason" or "Early Modern Philosophers" and "The Enlightenment"; another author might write from the perspective that 1600-1800 is essentially one continuous evolution, and therefore a single period. Wikipedia's philosophy section therefore hews more closely to centuries as a means of avoiding long discussions over periods, but it is important to note the variety of practice that occurs.

The 19th century took the radical notions of self-organization and intrinsic order from Goethe and Kantian metaphysics, and proceeded to produce a long elaboration on the tension between systematization and organic development. Foremost was the work of Hegel, whose Logic and Phenomenology of Spirit produced a "dialectical" framework for ordering of knowledge. The 19th century would also include Schopenhauer's negation of the will. As with the 18th century, it would be developments in science that would arise from, and then challenge, philosophy: most importantly the work of Charles Darwin, which was based on the idea of organic self-regulation found in philosophers such as Adam Smith, but fundamentally challenged established conceptions.

Also in the 19th century, the Danish philosopher Søren Kierkegaard took philosophy in a new direction by focusing less on abstract concepts and more on what it means to be an existing individual. His work provided impetus for many 20th century philosophical movements, including existentialism.

The philosophy of the present century is difficult to clarify due to its immaturity. A number of surviving 20th century philosophers have established themselves as early voices of influence in the 21st. These include Noam Chomsky, Saul Kripke, and Jürgen Habermas. The perceived conflict between continental and analytic schools of philosophy remains prominent, despite increasing skepticism regarding the distinction's usefulness. A variety of new topics have risen to the stage in analytic philosophy, orienting much of contemporary discourse in the field of ethics. New inquiries consider, for example, the ethical implications of new media and information exchange. Such developments have rekindled interest in the philosophy of technology and science. There has been increased enthusiasm for highly specialized areas in philosophy of science, such as in the Bayesian school of epistemology.

Indian philosophy primarily begins with the later part of Rig Veda, which was compiled before 1100 BCE.[2] Most of philosophy of the Rig Veda is contained in the sections Purusha sukta and Nasadiya Sukta. Vedas are followed by Upanishads; the oldest, such as the Brhadaranyaka and Chandogya Upanishads, have been dated to around the 8th century BCE. The philosophical edifice of Indian religions viz., Hinduism, Jainism, Buddhism is built on the foundation laid by the Upanishads. Upanishadic thoughts were followed by the Buddhist and Jain philosophies.

Confucianism can be considered as the oldest school of philosophy in China.[citation needed] Confucianism developed in China around the same time as Buddhism and Jainism developed in India. Another school of philosophy, Taoism, developed in China around 200 BC.[citation needed]

Abrahamic philosophy, in its loosest sense, comprises the series of philosophical schools that emerged from the study and commentary of the common ancient Semitic tradition which can be traced by their adherents to Abraham ("Father/Leader of many" Hebrew אַבְרָהָם ("Avraham") Arabic ابراهيم ("Ibrahim"), a patriarch whose life is narrated in the Hebrew Bible/Old Testament, and as a prophet in the Qur'an and also called a prophet in Genesis 20:7).

The standard text common to all of these subsequent tradition is known as the Hebrew Bible, roughly the first five books of the Old Testament, starting with the book of Genesis through to Deuteronomy. However, each of them added substantially different texts to their emerging canons, and hence their respective philosophical developments varied widely.

Islamic philosophy as Henry Corbin describes is a philosophy whose development, and whose modalities, are essentially linked to the religious and spiritual fact of Islam.[3] In the other word, it represents the style of philosophy produced within the framework of Islamic culture. This description does not suggest that it is necessarily concerned with religious issues, nor even that it is exclusively produced by Muslims.[4]

Theoretical questions were raised right from the beginning of Islam, questions, which could, to a certain extent be answered by reference to Islamic texts such as the Quran, the practices of the community and the traditional sayings of Muhammad, the Prophet of Islam, and his Companions.[4] In fact, rational arguments about Islamic doctrines starts with the Quran itself, and has been followed up in the utterances of the Muhammad and especially in the sermons of Ali. This despite the fact that their style and approach are different from those of the Muslim theologians.[5]

Though nothing definite can be said about the beginnings of theology among Muslims, what is certain is that discussion of some of the problems, such as the issue of predestination, free will and Divine Justice, became current among Muslims during the first half of the 2nd century of Islam coincides with 8th century. Perhaps the first formal centre of such discussions was the circle of Hasan al-Basri(d.728-29).[5] Later several theological schools have emerged from 8th to 10th century. Mu'tazili theology originated in the 8th century in Basra (Iraq) by Wasil ibn Ata (d.748 A.D.).[6]

The early conquests of the Muslims brought them into close contact with centers of civilization heavily influenced by Christianity and also by Greek culture. Many rulers wished to understand and use the Greek forms of knowledge, some practical and some theoretical, and a large translation project started which saw official support for the assimilation of Greek culture. This had a powerful impact upon all areas of Islamic philosophy. Neoplatonism definitely became the prevalent school of thought, following closely the curriculum of Greek philosophy which was initially transmitted to the Islamic world.[4]

The first period of Islamic philosophy coincides with Islamic golden age. During this time pure philosophical thought is usually used Aristotelianism and Neoplatonism thought as its sources. But it also influenced by Islamic thought and culture. Falaturi has shown in his research that how Hellenistic philosophy diverged in the context of Islamic culture. On the other hand Corbin has shown how mystic aspect of Islam, especially Shia affected philosophy. This period begins with al-Kindi and ends with Averroes (d.1198).[7] On the other hand there were crucial theological debates between Muslim theologians. These discussion also helped to rise of rational debates about religion, especially Islam.

Avicenna is one of the most prominent figures of this period. He is a thinker who attempted to redefine the course of Islamic philosophy and channel it into new directions. Avicenna's metaphysical system is built on the ingredients and conceptual building blocks which are largely Aristotelian and Neoplatonic, but the final structure is more than the sum of its parts.[8] In the Islamic Golden Age, due to Avicenna's successful reconciliation between Aristotelianism and Neoplatonism along with Islamic theology, Avicennism eventually became the leading school of early Islamic philosophy by the 12th century. Avicenna had become a central authority on philosophy by then.[9] Although this school was highly criticized by Muslim theologians, such as al-Ghazali, philosophers, like Averroes, and Sufis, Avicenna's writings spread like fire and continued until today to form the basis of philosophic education in the Islamic world. For to the extent that the post-Averroistic tradition remained philosophic, especially in the eastern Islamic lands, it moved in the directions charted for it by Avicenna in the investigation of both theoretical and practical sciences.[8]

After the death of Averroes, Islamic philosophy in the Peripatetic style went out of fashion in the Arab part of Muslim world, until the 19th century. Mystical philosophy, by contrast, continued to flourish, although no thinkers matched the creativity of Ibn Arabi or Ibn Sab‘in. In the Persian-speaking part, Islamic philosophy has continued to follow a largely Illuminationist curriculum, which is introduced by Suhrawardi.[4][7]

New trends have emerged during 19th and 20th centuries due to challenge of western philosophy and Modernity to traditional Islamic philosophy. On one hand some of the scholars such as Jamal-ad-Din Asadabadi and Muhammad Abduh sought to find rational principles which would establish a form of thought which is both distinctively Islamic and also appropriate for life in modern scientific societies, a debate which is continuing within Islamic philosophy today. Muhammad Iqbal is one of the prominent figure of this group who provided a rather eclectic mixture of Islamic and European philosophy. On the other hand some thinkers reacted to the phenomenon of modernity by developing Islamic fundamentalism. This resuscitated the earlier antagonism to philosophy by arguing for a return to the original principles of Islam and rejected modernity as a Western imperialist intrusion.[4] In Iran, the effects of mystic philosophers especially Mulla Sadra is great, and philosophers who are more loyal to traditional Islamic philosophy have tried to keep alive this school and use it to deal with Modernism. Allameh Tabatabaei is the most prominent figure of this group. [12] Nowadays Seyyed Hossein Nasr tries to introduce traditional Islamic philosophy and dealt with the Islamic response to the challenges of the modern world.[13] Finally, there have been many thinkers who have adapted and employed non-Islamic philosophical ideas as part of the normal philosophical process of seeking to understand conceptual problems such as Hegelianism and Existentialism. Therefore modern Islamic philosophy is thus quite diverse, employing a wide variety of techniques and approaches to its subjects.[14]

^Oberlies (1998:155) gives an estimate of 1100 BC for the youngest hymns in book 10. Estimates for a terminus post quem of the earliest hymns are more uncertain. Oberlies (p. 158) based on 'cumulative evidence' sets wide range of 1700–1100